Vacuum insulating glass (VIG) units typically include at least two spaced apart glass substrates that enclose an evacuated or low-pressure space/cavity therebetween. The substrates are interconnected by a peripheral edge seal and typically include spacers between the glass substrates to maintain spacing between the glass substrates and to avoid collapse of the glass substrates that may be caused due to the low pressure environment that exists between the substrates. Some example VIG configurations are disclosed, for example, in U.S. Pat. Nos. 5,657,607, 5,664,395, 5,657,607, 5,902,652, 6,506,472 and 6,383,580 the disclosures of which are all hereby incorporated by reference herein in their entireties.
FIGS. 1 and 2 illustrate a typical VIG window unit 1 and elements that form the VIG window unit 1. For example, VIG unit 1 may include two spaced apart substantially parallel glass substrates 2, 3, which enclose an evacuated low-pressure space/cavity 6 therebetween. Glass sheets or substrates 2,3 are interconnected by a peripheral edge seal 4 which may be made of fused solder glass, for example. An array of support pillars/spacers 5 may be included between the glass substrates 2, 3 to maintain the spacing of substrates 2, 3 of the VIG unit 1 in view of the low-pressure space/gap 6 present between the substrates 2, 3.
A pump-out tube 8 may be hermetically sealed by, for example, solder glass 9 to an aperture/hole 10 that passes from an interior surface of one of the glass substrates 2 to the bottom of an optional recess 11 in the exterior surface of the glass substrate 2, or optionally to the exterior surface of the glass substrate 2. A vacuum is attached to pump-out tube 8 to evacuate the interior cavity 6 to a low pressure, for example, using a sequential pump down operation. After evacuation of the cavity 6, a portion (e.g., the tip) of the tube 8 is melted to seal the vacuum in low pressure cavity/space 6. The optional recess 11 may retain the sealed pump-out tube 8. Optionally, a chemical getter 12 may be included within a recess 13 that is disposed in an interior face of one of the glass substrates, e.g., glass substrate 2. The chemical getter 12 may be used to absorb or bind with certain residual impurities that may remain after the cavity 6 is evacuated and sealed.
VIG units with fused solder glass peripheral edge seals 4 are typically manufactured by depositing glass fit, in a solution (e.g., frit paste), around the periphery of substrate 2 (or on substrate 3). This glass frit paste ultimately forms the glass solder edge seal 4. The other substrate (e.g., 3) is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers/pillars 5 and the seal material (e.g., glass frit in solution or paste), is then heated to a temperature of at least about 500° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic peripheral/edge seal 4.
After formation of the edge seal 4 between the substrates, a vacuum is drawn via the pump-out tube 8 to form low pressure space/cavity 6 between the substrates 2, 3. The pressure in space 6 may be produced by way of an evacuation process to a level below atmospheric pressure, e.g., below about 10−2 Torr. To maintain the low pressure in the space/cavity 6, substrates 2, 3 are hermetically sealed. Small high strength spacers/pillars 5 are provided between the substrates to maintain separation of the approximately parallel substrates against atmospheric pressure. As noted above, once the space 6 between substrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, for example, by melting its tip using a laser or the like.
A typical process for installing the pump-out tube 8 in the hole or aperture 10, includes inserting a pre-formed glass pump-out tube 8 in an aperture/hole 10 that has previously been formed (e.g., by drilling) in one of the glass substrates 2. After the pump-out tube 8 has been seated in the aperture/hole 10, an adhesive fit paste is applied to the pump-out tube 8, typically in a region close to the opening of the hole 10 proximate an exterior surface of the glass substrate 2. As noted above, the pump-out tube may be sealed after evacuation or purging of the VIG cavity.
After evacuation of the cavity to a pressure less than atmospheric, sealing of the pump-out tube may be accomplished by heating an end of the pump-out tube that is used to evacuate or purge the cavity to melt the opening and thus seal the cavity of the VIG window unit. For example and without limitation, this heating and melting may be accomplished by laser irradiation of the tip of the pump-out tube.
However, it has been found that application of laser energy to the tip of the pump-out tube can be controlled to achieve more reliable sealing. As noted above, a heat conduction problem from the end of the pump-out tube to the frit interface may result in undesirable cracking of the pump-out tube at the frit interface which may compromise the vacuum in the cavity of the VIG window unit. Faster laser processing may be used in an effort to reduce the exposure of the glass pump-out tube to the laser and reduce the time allowed for heat to conduct through the pump-out tube, and thus reduce the probability of heat conduction to the frit and potential cracking at the interface of the pump-out tube and the fit. However, fast constant/continuous laser processing in a single manner with high laser power suffers from the drawback of potentially super heating the glass of the pump-out tube and potentially boiling off the top layer of the glass pump-out tube. Significant outgassing may occur if the top layer of the glass pump-out tube is allowed to boil. This outgassing may undesirably decrease the vacuum already pumped down in the VIG window cavity, resulting in an undesirable decrease of the insulating (or “R”) value of the resulting VIG window unit. Therefore, what is needed is a way to seal the end of the glass pump-out tube so that sufficient energy is provided to melt the end of the tube, while at the same time avoiding boiling of the end of the glass pump-out tube during sealing to avoid potential detrimental outgassing. In addition, it is preferable to heat the end of the pump-out tube in such a way as to avoid cracking of the pump-out tube at the tube/frit interface.
To overcome these drawbacks a new way of sealing the end of the pump out tube is provided according to certain example embodiments disclosed herein. For example, instead of using a fast high-powered sealing process, a process using sequential multiple applications of laser energy using variable power settings, controlled exposure times and sequentially reducing a diameter of the laser path or trace provides a more controlled melting of the tube glass, resulting in lower outgassing according to certain example embodiments. While the process according to certain example embodiments is slower which may potentially result in greater heat conduction through the pump-out tube, the process is balanced with controlling the length of the pump-out tube as set forth above to control the distance from the top of the frit to the top of the pump-out tube. According to further example embodiments, a cycle of repeated exposure of the pump out tube to different energy levels of the laser for controlled times provides further advantages and helps to avoid or prevent outgassing. For example, and without limitation, a multi-cycle melting (or “tip off”) process may include a first pre-melt cycle, at least a second core heating cycle and a plurality of chase cycles that eventually melt and seal off the tip of the pump-out tube. Various combinations of power, repetitions and cycles may be implemented according to certain example embodiments disclosed herein.
These and other advantages are provided by a method of making a vacuum insulated glass window unit, the method comprising: providing a vacuum insulated glass window comprising: a first substrate having a pump-out tube disposed in a hole formed in the first substrate; a second substrate; and an edge seal, the first and second substrates arranged to sandwich the edge seal and form a cavity therebetween; sealing an end of the pump-out tube extending out of the first substrate, the sealing step comprising: performing at least one preheating treatment to clean a top of the pump-out tube and to begin heating the top of the pump-out tube; performing at least one core heating treatment to melt the top of the pump-out tube; and performing a plurality of chase treatments using successively reduced laser trace diameters to seal the tube.
These and other embodiments and advantages are described herein with respect to certain example embodiments and with reference to the following drawings in which like reference numerals refer to like elements, and wherein: